I'm creating this gist as I had a hard time locating a solution to my issue and I needed to perform multiple updates to the group assigned to a domain within the Group management functionality within Pi Hole.
Thanks to the post below for giving me ideas and pointing me in the right direction. Hopefully this functionality is added within the Web UI later on. https://discourse.pi-hole.net/t/group-management-multi-selection-of-domains-to-add-remove-delete-multiple-to-from-a-group-in-one-go/44671
We first need the ID of the group that we want to set the domains assigned to. You can view these groups in the SQLite DB by running